1. Technical Field of the Invention
The present invention relates to reflective and transflective liquid crystal devices which use silver alloys and the like to reflect light, to a method for making the same, and to electronic apparatuses using the liquid crystal devices as display sections.
2. Description of the Related Art
As is well known, liquid crystal devices do not emit light but performs display by controlling the polarization state of light. Thus, it is necessary that the configuration be such that light is incident on a panel of the liquid crystal device, and in this regard, they are quite different from other display devices, such as electroluminescent devices and plasma display devices.
Incidentally, the liquid crystal devices are classified into two types, that is, a transmissive type having a light source provided behind a panel such that the light passing through the panel can be observed by a viewer, and a reflective type in which a light source is arranged at the front side of the panel (or is not arranged) and the light incident from the front face is reflected by the panel and can be observed by a viewer.
In the transmissive type, the light emitted from the light source provided at the rear side of the panel is introduced to the entire panel through a light guide plate. Then, the light passes through a polarizer, a back substrate, an electrode, a liquid crystal, another electrode, a viewer-side substrate, and another polarizer and is observed by the viewer.
On the other hand, in the reflective type, the light incident on the panel passes through a polarizer, a viewer-side substrate, an electrode, a liquid crystal, and another electrode, is reflected by a reflective film, and passes through the path in the reverse direction, and is observed by a viewer.
As described above, the reflective type needs two paths including an incident path and a reflected path and large optical losses occur in both paths. Compared to the transmissive type, the amount of light from the surrounding environment (external light) is less than that of a light source disposed at the rear side of the panel. Since only a small amount of light is observed by the viewer, the display becomes dim. However, the reflective type also has noticeable advantages, such as high outdoor visibility under sunlight and an ability to display without a light source, compared with the transmissive type. Thus, the reflective liquid crystal display devices are widely used in display sections of portable electronic apparatuses and the like.
The reflective type, however, has a notable disadvantage in that the viewer cannot see the display when insufficient natural illumination is provided from the environment. In recent years, a transflective type has appeared in which a backlight is provided at the rear face of a panel, and a reflective film not only reflects the light incident from the viewer""s side but also transmits some of the light from the rear face. This transflective type functions both as a transmissive type by switching on the backlight to ensure visibility of the display when there is insufficient external light and as a reflective type by switching off the backlight in order to reduce power consumption when there is sufficient external light. This means, the transmissive type or the reflective type is selected depending on the intensity of the external light to ensure visibility of the display and to reduce power consumption.
In the reflective type and the transflective type, aluminum has been generally used as a material for the reflective film. However, in recent years, the use of elemental silver or a silver alloy primarily composed of silver (hereinafter referred to as merely xe2x80x9csilver alloyxe2x80x9d) has been investigated to improve reflectance for achieving bright display.
It is not desirable that one electrode used for applying a voltage to the liquid crystal is also used as a reflective layer to simplify the configuration. When this electrode is formed of the silver alloy and the other electrode is formed of a transparent conductive material such as indium tin oxide (ITO) which meets the transparency requirement, irregularity of polarization occurs by sandwiching the liquid crystal with different metals. Furthermore, in a configuration in which only an alignment film is present between the liquid crystal and the silver alloy, impurities in the silver alloy are dissolved into the liquid crystal through the alignment film, and may cause deterioration of the liquid crystal itself.
Thus, the electrode on the substrate provided with the reflective layer cannot be formed of the silver alloy and must be formed of the same transparent conductive material which is used as the electrode of the other substrate. Accordingly, the substrate provided with the reflective layer must use at least two metals, that is, the silver alloy used as the reflective layer and the transparent conductive material as the electrode.
Incidentally, the silver alloy exhibits high conductivity, in addition to high reflectance, and the use thereof as a lead layer of the substrate is being investigated. When the silver alloy used as the reflective layer is also used as the lead layer, the silver alloy must be put into contact with the transparent conductive material used as the electrode for electrical connection therebetween.
Since the silver alloy exhibits poor adhesiveness to other materials, the alloy is damaged by mechanical friction and moisture penetrating from the interface causes corrosion, separation, and the like. As a result, it is difficult to complete a highly reliable liquid crystal display device.
Accordingly, the object of the present invention is to provide a liquid crystal device having high reliability when a silver alloy is used as both a reflective layer and a lead layer, a method for making the same, and an electronic apparatus.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises an underlying film provided on the first substrate, a reflective conductive film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the reflective conductive film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. According to this configuration, the reflective conductive film is covered by the metal oxide film and the metal oxide film is patterned so that the edge portion thereof comes into contact with the underlying film; hence, the surface of the reflective conductive film is not exposed after the metal oxide film is formed. Thus, the reliability of the reflective conductive film containing silver is improved.
Preferably, the underlying film comprises a metal oxide. The reflective conductive film is thereby sandwiched by the two metal oxides. Since the metal oxides have high adhesiveness, moisture barely penetrates into the reflective conductive film through the interface between the underlying film containing the metal oxide and the metal oxide film deposited on the reflective conductive film.
Incidentally, the reflectance vs. wavelength relationship of the reflective conductive film containing silver is not so flat as that of aluminum (Al) which is generally used, and tends to decrease at the shorter wavelength end (see to FIG. 7). As a result, the light reflected by the reflective conductive film less contains the blue light component and thus is yellowish. Thus, a reflective layer reflecting blue light is preferably provided on the upper face of the reflective conductive film. As a result of such a configuration, large amounts of blue light components are reflected by the reflective layer before the blue light component is reflected by the reflective conductive film, preventing that all light reflected by the reflective layer and the reflective conductive film containing silver is yellowish.
Since an electronic apparatus in one aspect of the present invention is provided with the above liquid crystal device, reliability of the device is improved.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises a first lead provided on the first substrate, a conductive film provided on the second substrate, and a conductive material connecting the first lead and the conductive film, wherein the first lead comprises an underlying film, a metal film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the metal film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. Since the conductive film provided on the second substrate is connected to the first lead provided on the first substrate through the conductive material according to this configuration, all leads are arranged on the first substrate. Since the first substrate has the metal film containing silver, the resistance thereof is decreased. In addition, the metal film containing silver is covered by the metal oxide film and the metal oxide film is patterned so that the edge portion thereof comes into contact with the underlying film; hence, the surface of the metal film is not exposed after the metal oxide film is formed. Thus, the reliability of the metal film containing silver is improved.
In this configuration, the underlying film preferably comprises a metal oxide, because moisture barely penetrates into the reflective conductive film as described above. Preferably, the metal film is formed at a portion other than the connection to the conductive material. Since the silver alloy has poor adhesiveness, it is undesirable to provide the silver alloy at a portion in which stress is applied.
Preferably, the liquid crystal device further comprises a pixel electrode provided on the first substrate, an active element connected to the pixel electrode at one end of the active element, a signal line provided on the first substrate and connected to the first lead to apply a voltage to the liquid crystal, wherein the signal line is connected to the other end of the active element. According to this configuration, the pixel electrode is independently driven by the active element.
Preferably, the liquid crystal device further comprises a driver IC chip for driving the liquid crystal, wherein the driver IC chip comprises an output bump for supplying an output signal to the first lead, and the output bump is connected to the first lead. By mounting the driver IC chip for supplying the output signal to the first lead, the number of the connections to an external circuit can be reduced.
When the driver IC chip is mounted, the metal film of the first lead is preferably formed at a portion other than the connection to the output bump. Since the silver alloy exhibits poor adhesiveness, it is undesirable to provide the silver alloy at a portion in which stress is applied. In particular, when the substrate is detached from the first substrate to repair the driver IC chip, separation of the metal film containing silver may occur.
The liquid crystal device preferably further comprises a second lead provided on the first substrate and a driver IC chip for driving the liquid crystal, wherein the driver IC chip comprises an input bump for inputting an input signal from the second lead, the input bump is connected to the second lead, and the second lead comprises an underlying film, a metal film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the metal film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. Since the second lead has the metal film containing silver according to this configuration, the resistance of the second lead is reduced and the surface of the metal film is not exposed, high reliability is achieved. When an driver IC chip is mounted, the metal film of the second lead is preferably formed at a portion other than the connection to the input bump, in order to prevent separation of the metal film containing silver when the driver IC chip is repaired.
Moreover, the liquid crystal device preferably further comprises an external circuit board for supplying an input signal to the driver IC chip, wherein the external circuit board and the second lead are connected to each other, and the metal film is formed at a portion other than the connection to the external circuit board. This configuration prevents separation of the metal film containing silver when the external circuit board is repaired.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises an electrode provided on the first substrate for supplying a voltage to the liquid crystal, a first lead connected to the electrode, and a driver IC chip connected to the first lead, wherein the first lead comprises an underlying film, a metal film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the metal film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. Since the first lead includes the metal film containing highly conductive silver in such a configuration, the resistance thereof is reduced. Moreover, the metal film containing silver is covered by the metal oxide film and the edge portion of the metal oxide film is patterned so as to come into contact with the underlying film. Thus, the surface of the metal film is not exposed after the metal oxide film is formed. Accordingly, the reliability of the metal film containing silver is improved.
Preferably, the metal film is formed at a portion other than the connection to the driver IC chip, in order to prevent separation of the metal film containing silver when the driver IC chip is repaired.
Preferably, the liquid crystal device further comprises a second lead provided on the first substrate, wherein the driver IC chip comprises an input bump for inputting an input signal from the second lead, the input bump is connected to the second lead, and the second lead comprises an underlying film, a metal film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the metal film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. According to this configuration, the resistance of the second lead, in addition to the first lead, is reduced, and the surface of the metal film containing silver is prevented from exposure.
Also, in this configuration, the liquid crystal device preferably further comprises an external circuit board for supplying an input signal to the second lead, wherein the metal film is formed at a portion other than the connection to the external circuit board, in order to prevent separation of the metal film containing silver when the driver IC chip is repaired.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises a lead provided on the first substrate, wherein the lead comprises an underlying film, a metal film formed on the underlying film, and a metal oxide film deposited on the metal film.
In this liquid crystal device, preferably, the underlying film comprises a metal oxide, and the metal film comprises elemental silver or a silver alloy. Preferably, the liquid crystal device further comprises a first extending region which is provided at one side of the first substrate and which does not overlap the second substrate, and a second extending region which is provided at a side crossing said one side of the first substrate and which does not overlap the second substrate, wherein the lead is provided over the first extending region and the second extending region.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises: an underlying film provided on the first substrate, a reflective conductive film which is formed on the underlying film and which contains silver, a first transparent electrode deposited on the reflective conductive film and comprising a metal oxide film which is patterned so that the edge portion of the first transparent electrode comes into contact with the underlying film, a second transparent electrode provided on the second substrate, and a transflective portion provided corresponding to the crossing between the first transparent electrode and the second transparent electrode. According to this configuration, a transflective type device is achieved while the reliability of the reflective conductive film containing silver is ensured.
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises an underlying film provided on the first substrate, a reflective conductive film which is formed on the underlying film and which contains silver, a first transparent electrode deposited on the reflective conductive film and comprising a metal oxide film which is patterned so that the edge portion of the reflective conductive film comes into contact with the underlying film, a second transparent electrode provided on the second substrate, and a color layer provided corresponding to a crossing between the first transparent electrode and the second transparent electrode. This configuration enables color displaying while the reliability of the reflective conductive film containing silver is ensured.
In accordance with an aspect of the present invention, in a method for making a liquid crystal device which comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, the method comprises the steps of forming an underlying film on the first substrate, forming a reflective conductive film containing silver on the underlying film, and forming a metal oxide film on the reflective conductive film so that the edge portion of the reflective conductive film comes into contact with the underlying film. According to this method, the reflective conductive film is covered by the metal oxide film and the edge portion of the metal oxide film is formed so as to come into contact with the underlying film. Thus, the surface of the reflective conductive film is not exposed, improving the reliability of the reflective conductive film containing silver.
In this method, the underlying film preferably comprises a metal oxide. Moisture or the like barely penetrates into the reflective conductive film.
Preferably, the method further comprises the step of simultaneously patterning the underlying film and the metal oxide film. This method contributes to a reduction in manufacturing step.